Development of monomolecular, oligomeric and polymeric carbazole compounds as photosensitizers for photoinitiated cationic polymerization

Enhancement of the rates of onium salt photoinitiated cationic polymerization of epoxide and vinyl ether monomers has been observed through the use of carbazole compounds. It was demonstrated that various carbazole-containing compounds and polymer/copolymers are effective electron-transfer photosensitizers. The photosensitizable cationic onium salt initiators include diaryliodonium, triarylsulfonium, and dialkylphenacylsulfonium salts.; In the presence of large amount of N-vinyl carbazole (NVK), the rate of photoinitiated cationic polymerization of epoxide and vinyl ether monomers was more significantly increased compared with the presence of small amounts of (<2% based on monomer) carbazole compounds and this effect was not observed with other carbazole compounds. The effect was ascribed to a photoinitiated free-radical chain reaction that results in the oxidation of N-vinyl carbazole by the onium salt initiators to generate cations. These cations can initiate the polymerization of epoxide and vinyl ether monomers, leading to the production of copolymers.; Poly(N-vinylcarbazole) (PVK) is an especially attractive and efficient photosensitizer. PVK functions as an electron-transfer photosensitizer for a variety of onium salt cationic photoinitiators. Alternating copolymers prepared by the free radical copolymerization of N-vinylcarbazole (NVK) with vinyl monomers also exhibit excellent photosensitization activity. The broadening of the spectral response through the use of these photosensitizers accounts for the observed rate enhancement of these polymerization systems. Also studied is the synthesis and use of a dimeric photosensitizer prepared by the hydrosilation of NVK with 1,1,3,3-tetramethyldisiloxane.; Other monomers that contain both carbazole group and cationic polymerizable groups were studied. These monomers were efficiently photopolymerized in the presence of onium salt photoinitiators. The photosensitization effect of these monomers and polymers was also investigated. The inclusion of a small amount of these monomers and polymers prepared by the polymerization of the monomeric photosensitizers markedly accelerated the photopolymerization of cationic monomers. This effect was ascribed to the electron-transfer photosensitization by these monomers and polymers.